How Do Microstructure and PREN Affect the Erosion Corrosion Behaviour of Stainless Steels?

A combined flow loop - jet impingement pilot plant has been used to determine mass loss rates in a mixed gas - saltwater - sand multiphase flow at impact velocities up to 60 m/s. Artificial brine with a salt content of 27 g/l was used as liquid phase. Sand content with grain size below 150 µm was up to five times higher than field conditions to accelerate testing. CO₂ at a pressure of 15 bar was used as gas phase.
Rectangular stainless steel samples were cut out from bars and pipes, mechanically ground and polished prior to testing. Damaged surfaces of specimens exposed to the high velocity multiphase flow were investigated by stereo microscopy, scanning electron microscopy (SEM) and an optical device for 3D surface measurements. Metallographic cross sections of the tested samples were prepared to characterize the microstructure underneath the damaged surface areas. Moreover electrochemical investigations according to ASTM G 61 were performed to determine electrochemical behavior of tested materials including critical pitting potentials E_pit and protection potentials E_prot.
Influence of impact velocity on mass loss rates (penetration rates) of austenitic, martensitic and duplex stainless steel grades are presented. Effects of chemical composition, PREN, microstructure and mechanical properties are critically discussed.